1. Field of the Invention
The present invention relates to a movable electrical contact assembly forming a potentiometer and including a movable electrical contact and at least one stationary contact having significant resistance. Preferably, the movable contact is a movable or rollable conductive element that is urged against and rolls along the stationary contacts.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn. 1.97-1.99
Electrical contact between moving parts is subject to friction and wear. From a mechanical point of view, high contact pressure results in high friction and consequently, severe wear. The frictional resistance of sliding one metal contact over another metal contact is due mainly to the shearing of welded junctions that are formed when the surfaces are placed in contact under load. The upper metal contact is supported on the peaks of surface irregularities on the lower metal contact, so that the real area of contact is very small. The intense local pressures produce welded junctions, even at light loads, and plastic deformation takes place until the total area over which welding occurs is sufficient to support the load without further deformation. This shearing of the welded junction is the main cause of frictional resistance. The magnitude of this effect depends on the melting points of the two metals. Small particles of metal are often detached from the sliding metal contact and adhere to the other metal contact.
It is well known from the knowledge of mechanics and experience with wear that a rolling contact produces much less wear than that of a sliding contact. However, a rolling contact has been rarely used in electric contact designs for the reasons that hard roller contacts with a hard surface basically form a line contact which can hardly produce a sufficient contact surface area under a reasonable pressure since the cylindrical configuration of the hard roller does not result in a large contact area. On the other hand, a sliding brush can be designed in an optimized configuration to produce maximum contact area under pressure. Therefore, a brush has been more desirable where contact area is concerned and it is more frequently used in practice despite the fact that it relies on sliding motion and causes more wear.
The Jones U.S. Pat. No. 3,859,488 teaches a roller band electrical switching mechanism wherein one or both of the rollers serves as a movable contact. The roller or rollers function as a contact supported and guided directly by a hollow case. The roller support and guide surfaces, or races, of the case are concavely curved and incorporate fixed contacts which have been exposed surfaces which lie flush with the roller guide surface of the case. The roller, with its ends in substantial rolling point engagement with the races, closes or opens electrical circuits as it rolls along the guide surface. The roller band in most cases does not touch the case. By thus suspending the roller so that it can serve as a movable contact, exerting great localized pressure on embedded contacts flush with the rolling support surface while producing minimal switching friction, a substantial increase of switching quality and utility is achieved.
The Tackett U.S. Pat. No. 4,139,071 teaches a roadway for automotive vehicles including means for transmitting electric current through the road surface to electrically operated vehicles travelling thereon. The vehicle employs electrically-conductive tires which roll on an electrically-conductive surface of the contact assembly, and the current thus picked up is transmitted, through rolling-sliding contacts, conductors, etc. in contact with the tires to controls for controlling the vehicle through individual wheel motors. The contact member rolls on an annular track of the tire for receiving the current while the contact member is sliding on a shaft for conducting the current into the system.
The movable electrical contact assembly of the present invention differs from the previously proposed electrical contact assemblies by including at least one conductive strip, which has a significant resistance, and a deformable rolling contact element in rollable contact with the conductive strip.